Kinetics, electrochemistry and resonance raman spectra of the (2-mercaptopyridine) (edta)ruthenium(III) complex

The chemistry of the pentadentate edta complexes of ruthenium(III) and (II) with 2-mercaptopyridine (HSpy) has been investigated based on spectroscopic, kinetic and electrochemical techniques. The reaction of [Ru(III)(edta)H2O]- with HSpy proceeds with a specific rate of 1.05 × 104 M-1 S -1 (25°C, I = 0.10 M, acetate buffer), forming a red complex (λmax = 550 nm) which undergoes a relaxation process as a function of pH, with an apparent pKa = 4.35 and kobs = 0.31 S -1. The second reaction depends on the concentration of HSpy and leads to a stable green product (λmax = 630 mn). A pronounced enhancement has been observed in the Raman spectra of the complexes, particularly in the region of the metal-ligand vibrations. The electronic and resonance Raman spectra are consistent with the coordination of HSpy via the sulfur atom in the red complex, and with a chelate binding in the green species. © 1987.

Observed supersymmetry in baryon and meson spectra with IBFM, the interacting Boson-fermion model

Supersymmetry is already observed in (i) nuclear physics where the same empirical formula based on a graded Lie group described even-even and odd-even nuclear spectra and (ii) in Nambu-BCS theory where there is a simple relationship between the energy gap of the basic fermion and the bosonic collective modes. We now suggest similar relationships between the large number of mesonic and baryonic excitations based on the SU(3) substructure in the U(15/30) graded Lie group.

Synthesis, structure, and electronic and EPR spectra of copper(II) complexes containing the [CuBr4]2- anion and triphenylarsine oxide

The preparation and characterization of (Ph3AsOH)2[CuBr4] and [Cu(Ph3AsO)4][CuBr4] are reported (Ph3AsO = triphenylarsine oxide). Crystallographic analysis of the monoclinic crystals of (Ph3AsOH)2[CuBr4] (space group C2/c, a = 17.569 (3) Å, b = 13.090 (2) Å, c = 16.933 (2) Å, and β = 105.64 (2)°, R = 0.055 and Rw = 0.057) revealed the presence of compressed [CuBr4]2- tetrahedra of C2 symmetry with Cu-Br distances of 2.340 (1) and 2.437 (1) Å and trans-Br-Cu-Br angles of 139.2 (1) and 122.4 (1)°. The oxonium cations hydrogen bond to the bromine atoms involved in the longer Cu-Br bonds and the smaller trans-Br-Cu-Br angle. Single-crystal electronic and EPR spectra are interpreted in terms of the observed [CuBr4]2- geometry. Analysis of the electronic and EPR spectra of [Cu(Ph3AsO)4][CuBr4] led to the postulation of the presence of planar [Cu(Ph3AsO)4]2+ cations and distorted tetrahedral [CuBr4]2- anions. © 1992 American Chemical Society.

Spectroscopic characterization of SnO2 gels - Code: CP11

Excitation and dynamic emission spectra of Eu3+ ions were simultaneously used with FTIR and Raman spectroscopy to study the structural evolution during SnO2 sol → gel → xerogel conversion. Results make evident an increase of the surroundings symmetry for the Eu3+ ions dissolved in SnO2 matrix and a decrease of the amount of hydroxo groups (Sn-OH) during drying. These phenomena were associated to the pursuit of the condensation reaction after gelation. © 1994 Kluwer Academic Publishers.

Theoretical investigation of the electronic structure and absorption spectra of carbon cluster nanotubes

Electronic and optical properties of recently discovered single-shell carbon cluster nanotubes are studied through a semiempirical INDOCI method. The calculations are performed within the cluster model and include up to 196 atoms. The trend of the forbidden band gap with the number of carbon atoms (Cn n = 60, 10, 140) for a fixed diameter is analyzed. With increasing n the band gap decreases, as expected. The tubule, with diameter of 7.2Å (as C60-Buckyball) is predicted to be a metal or a narrow-gap semiconductor. The calculated absorption spectra of the clusters show a characteristic strong peak around 40,000 cm-1. Other features of the calculated UV-visible absorption spectra are discussed. © 1994.

Niobium filtration of conventional and high-frequency x-ray generator beams for intraoral radiography. Effects on absorbed doses, image density and contrast, and photon spectra

We have studied the effects of niobium beam filtration on absorbed doses, on image density and contrast, and on photon spectra with conventional and high-frequency dental x-ray generators. Added niobium reduced entry and superficial absorbed doses in periapical radiography by 9% to 40% with film and digital image receptors, decreased the radiation necessary to produce a given image density on E-speed film and reduced image contrast on D- and E-speed films. As shown by increased half-value layers for aluminum, titanium, and copper and by pulse-height analyses of beam spectra, niobium increased average beam energy by 6% to 19%. Despite the benefits of adding niobium on patient dose reduction and on narrowing the beams' energy spectra, the beam can be overhardened. Adding niobium, therefore, strikes the best balance between radiation dose reduction and beam attenuation, with its risks of increased exposure times, motion blur, and diminished image contrast, when it is used at modest thicknesses (30 μm) and at lower kVp (70) settings. © 1995 Mosby-Year Book, Inc.

Light and thermal excitation of depolarization current in indirect bandgap Alx Ga1-xAs

Monochromatic light excitation in conjunction with thermally stimulated depolarization current measurements are applied to indirect bandgap AlxGa1-xAs. The obtained average activation energy for dipole relaxation is in very close agreement with the DX center binding energy. Monochromatic light induces state transition in the defect and makes possible the identification of dipoles observed in the dark. Charge relaxation currents are destroyed by photoionization of Al0.5Ga0.5As using either 647 nm Kr+ or 488 nm Ar+ laser lines, which are above the DX center threshold photoionization energy. It suggests that correlation may exist among charged donor states DX--d+. Sample resistance as a function of temperature is also measured in the dark and under illumination and shows the probable X valley effective mass state participation in the electron trapping. Ionization with energies of 0.8 eV and 1.24 eV leads to striking current peak shifts in the thermally stimulated depolarization bands. Since vacancies are present in this material, they may be responsible for the secondary band observed in the dark as well as participation in the light induced recombination process.

Frequency upconversion in Nd3+-doped fluoroindate glass

We report the observation of frequency upconversion in fluoroindate glasses with the following compositions: (mol%) (39 - x)InF3-20ZnF2-20SrF2-16BaF 2-2GdF3-2NaF-1GaF3-xNdF3 (x = 0.05, 0.1, 0.5, 1, 2, 3). The excitation source was a dye laser in resonance with the 4I9/2→(2G5/2, 2G7/2) transition of the Nd3+ ions. The upconverted fluorescence spectra show emissions from ∼ 350 to ∼ 450 nm, corresponding to transitions 4D3/2→4I9/2 ;4D3/2→4I11/2; 2P3/2→ 4I9/2; 4D3/2→4I13/2; 2P3/2→4I11/2; 4D3/2→4I15/2; and 2P3/2 → 4I13/2. The dependence of the fluorescence signals on the laser intensity indicates that two laser photons participate in the process. The temporal behavior of the signal indicates that energy transfer among the Nd3+ ions is the main mechanism which contributes to upconversion at 354 and 382 nm.

Description of inclusive meson spectra in e+e- annihilation reactions by a quark cascade model

We present a model to describe inclusive meson production in e+e- reactions based on a quark cascade approach whose formulation is put in terms of diffusion equations for three quark flavors (u, d, s). These equations are solved by using a formalism previously developed for the problem of the electromagnetic cascade generated in the atmosphere by cosmicray interactions. The obtained solutions are given in terms of a combination of power-law functions whose profiles are adequate to describe the characteristics observed in the inclusive spectrum of mesons.

New results on bound excitons in quantum wells

The formation of bound excitons (BE) is investigated for a GaAs/GaAlAs multiple quantum well (QW) system. The photoluminescence (PL) spectra are analysed as a function of the excitation energy. It was found that the carriers photogeneration, either in the barrier or directly in the well, do not play an important role on the BE formation. We conclude that defects localized at interfaces are ionized by of capture charges which in turn bound the free exciton (FE).

Synthesis, characterization and spectroscopy of the europium doped lanthanum trimetaphosphate

Orthorhombic modification of europium doped lanthanum trimetaphosphate has been prepared. The compound was obtained by precipitation of rare earth chloride solution with trimetaphosphoric acid. The characterizations were made using X-ray diffractometry, chemical analysis and infrared spectroscopy. Excitation and emission spectra were recorded at liquid nitrogen and room temperatures. Assignments of the 5D0→7FJ (J=0, 1, 2, 3, 4, 5) transitions were made and an unusual high 5D0→7F4 transition intensity with six split lines has been observed. Structural distortion of the crystal lattice may be caused by the Eu3+ ion inclusion. The simple overlap model was applied for the calculation of the total splitting of the 5D0→7F1 transition, the 5D0→7F0/5D 0→7F2 transition intensity ratio and the Ωλ (λ=2.4) intensity parameters. Theoretical predictions showed to be in good accordance with the experimental data. © 1988 Elsevier Science S.A.

Preparation, characterization and spectroscopy of the europium diphenylphosphinate complex

The purpose of this work is to study the preparation and spectroscopic behavior of the europium diphenylphosphinate complex -Eu(DPP)3. Elemental and thermogravimetric analysis, powder X-ray diffractometry, and infrared spectroscopy were applied to characterize the formula of the final product and the sixfold coordination of the Eu3+ ion. Excitation and emission spectra have been recorded at liquid nitrogen and room temperatures. The 5D0→7F2 transition intensity decreases when T decreases in comparison to the 5D0→7F1 transition intensity. Molecular mechanic calculations were developed in order to obtain the spatial coordinates of the Eu3+ and ligand ions. The simple overlap model was used to calculate the total splitting of the 5D0→7F1 transition, 5D0→7F0/5D 0→7F2 ntensity ratio and the intensity parameters, Ωλ (λ=2 and 4). Good agreements between theoretical predictions and experimental results have been obtained with g=2/3 as the effective charge and α=0.8×10-24 cm3 as the isotropic polarizability of the oxygen. © 1998 Elsevier Science S.A.

Gel'fand-Levitan equation for deletion of states from Coulomb spectra

The Gel'fand-Levitan formalism is used to study how a selected set of bound states can be eliminated from the spectrum of the Coulomb potential and also how to construct a bound state in the Coulomb continuum. It is demonstrated that a sizeable quantum well can be produced by deleting a large number of levels from the s spectral series and the edge of the Coulomb potential alone can support the von Neumann-Wigner states in the continuum. © 1998 Elsevier Science B.V.

Raman scattering study of zincblende InxGa1-xN alloys

We report on first-order micro-Raman and resonant micro-Raman scattering measurements on c-InxGa1-xN (0 ≤ x ≤ 0.31) epitaxial layers. We have found that both, the transverse-optical (TO) and longitudinal-optical (LO) phonons of InxGa1-xN alloy exhibit a one-mode-type behavior. Their frequencies at Γ lie on straight lines connecting the corresponding values obtained for the c-GaN and c-InN binary compounds. Evidence for phase separation is shown in the sample with the alloy composition x = 0.31. The Raman spectra, with excitation energy close to 2.4 eV, show an enhanced additional peak, with frequency between the values found for the LO and TO phonon modes of the C-In0.31Ga0.69N epitaxial layer. We ascribed this peak to the LO phonon mode of a minority phase with In content of ≈0.80.

Oxygen related defects excitation and photoconductivity dependence of SnO2 sol-gel films with several light sources

Since oxygen vacancies act as donors in SnO2, the electrical properties are related to deviation from stoichiometric composition. Depending on stoichiometry SnO2 can be highly insulating or may exhibit fairly high n-type conductivity. Since bandgap transitions are in the ultraviolet range, its photoconductivity is strongly dependent on the excitation source. We have measured variation of photoconductivity excitation with wavelength for tin dioxide grown by dip-coating sol-gel technique using several light sources: tungsten lamp, xenon, mercury and deuterium, and present selected results. The main band is obtained in the range 3-4eV according to light source spectrum in the ultraviolet range. The presence of oxygen in the cryostat also affects the spectrum since electron-hole pairs react with adsorbed oxygen specimens. © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.